Sawtooth voltage generator



Aug. 18, 1959 R. L. KUEHN ETAL 2,900,502 SAWTOOTH VOLTAGE GENERATORFiled May 21, 1956 C2 R3 R2 2 I Rudolph L. Kuehn Robert K. SeigleINVENTORS ATTORNEY and) SAWTOOTH VOLTAGE GENERATOR Rudolph L. Kuehn andRobert K. S eigle, Pasadena, Calif.,

assignors, by mesne assignments, to Hymac Corporation, Los Angeles,Calif., a corporation of California Application May 21, 1956, Serial No.586,287 6 Claims. 01. 250-27 The present invention relates generally tosweep generators and more particularly to a sawtooth voltage generatorcapable of both synchronized astable and triggered monostable operation.

The internal sweep generator of an oscilloscope, for example, can beeither astable (free-running) and synchrom'zed by various generatedsignals, or it can be monostable (one-shot) and be triggered by incomingsignals. The latter mode of operation is highly desirable since itinsures positive synchronization with little tendency to jitter and isexclusively used in the analysis of transient and pulse phenomena.

During the fly-back interval of an oscilloscope sweep cycle, thefluorescent electron beam spot produces a return trace on the cathoderay tube screen. This return trace does not contribute to the analysisof the waveform or pattern being examined but only serves to clutter thescreen. It is desirable to blank out the return trace that exists priorto each retrace sweep.

It is an object of this invention to provide a sawtooth voltagegenerator which is capable of both recurrent, free-running operation andtriggered monostable operation.

Another object of the invention is to provide a sawtooth voltagegenerator which can be easily synchro nized in recurrent (free-running)operation.

Another object of this invention is to provide a sweep generator forOscilloscopes, for example, which provides blanking of the return trace.

A further object of this invention is to provide a sawtooth generatorwhich is simple of construction and is readily useful as a sweepgenerator for oscilloscopes, for example.

The foregoing and other objects are preferably accomplished, briefly, byproviding two electronic tubes connected to form a modified cathodecoupled multivibrator having an input connection to one tube foraccepting synchronizing and trigger signals, and a storage capacitorconnected to the other tube for control of the latter tube and toprovide an output signal therefrom. Another output signal is obtainedfrom the latter tube to provide a suitable blanking signal foroscilloscopes, for example. Means connectable to the storage capacitorprovide triggered monostable operation of the multivibrator.

The invention possesses other objects and features, some of whichtogether with the foregoing, will'be set forth in the followingdescription of a preferred embodiment of the invention, and theinvention will be more fully understood by reference to the followingaccompanying drawings, in which: 7

Figure 1 is a schematic wiring diagram of a preferred embodiment of theinvention.

Figure 2 is a drawing showing a series of three curves of the voltagewaveforms which can be applied to and occur at different points of thecircuit.

A preferred embodiment of the invention is shown in Figure 1 of theaccompanying drawings. Two

ite States Patent electronic tubes V1 and V2 are connected to form amodified cathode coupled multivibrator. The tube V1 is preferably apentode and V2 can be a triode as illustrated. In actual practice, thesetwo tubes are usually combined in a single envelope and are readilyavailable on the market as such.

The cathodes of V1 and V2 are connected together to ground throughcathode resistor R1. The control grid and anode of V2 are respectivelyconnected to a source B+ of positive potential through resistors R2 andR3. Similarly, the screen grid and anode of V1 are connected to thissame source B+ through resistors R4 and R5, respectively. The controlgrid of V1 is connected to the anode of V2 through a resistor R6 and toground through resistor R7. Likewise, the control grid of V2 is alsoconnected to ground, but through a capacitor C1. The control grid of V2can be connected to the anode of V1 by a small capacitor C2 to provideneutralization of high frequency components in the synchronizingwaveform and thus prevent cross coupling to the sweep sawtooth.

A diode D having its cathode connected to another source +B1 of positivevoltage can be connected by switch S to the control grid of V2 andcapacitor C1 as shown. The anode of V2 is connected to a first outputterminal 1, and a second output terminal 2 is obtained at the commonjunction of resistor R2 and capacitor C1. An input terminal 3 isconnected to the screen grid of V1. Negative voltage impulses can beapplied to this input circuit for synchronization or triggering of thegenerator.

Operation of the circuit can be described with reference to Figure 2which illustrates the voltage waveforms e e and e that appear onterminals 1, 2 and 3, respectively. Curves 1a, 2a and 311 respectivelydepict the waveforms of e 2 and e;;. In recurrent or free-runningoperation, the switch S is open as shown, and V1 can be consideredinitially conducting because of a positive grid voltage across resistorR7. The accompanying cathode current produces a voltage drop acrossresistor R1 sufficient to bias V2 to cutoff. At the same time, capacitorC1 begins to charge toward B+ voltage through resistor R2. This isillustrated by the initial rising portion a of the center curve 2a ofFigure 2. When this voltage across C1, which furnishes grid voltage toV2, reaches the proper point, corresponding to the conduction level ofV2 as indicated by the broken line of curve 2a, V2 conducts.

The flow of V2 plate current through R3 produces a potential drop atterminal 1, and at the control grid of V1. R6 and R7 are so proportionedthat this voltage drop at the grid cuts off V1. Conduction through V2discharges the voltage across C1, as represented at b in the middlecurve of Figure 2. The plate voltage at terminal 1 is low during thedischarge interval of C1 (see curve 1a, Figure 2). When the voltageacross C1 has dropped to a sufliciently low value such that the voltageon the grid of V1 due to plate voltage rise in V2 now permits V1 toconduct, and since the voltage across C1 is now also below the value forconduction through V2, the cycle has been completed. Conduction of V1and cutofi of V2 will again allow capacitor C2 to start charging towardB-lvoltage through resistor R2, repeating the cycle. This recurrentoperation will continue as long as the circuit is energized.

In oscilloscope work, for example, it usually is desirable tosynchronize the sweep generator with an externally applied signal bymeans of a trigger impulse. A negative impulse voltage as shown in thelower curve 3a can be applied to terminal 3 and thence to the screengrid of V1 as a synchronizing signal and functions to cut off conductionin V1, and simultaneously lower the cathode potential of V2. CapacitorC1 has been charging toward B+ during the time that V1 was conducting,raising the grid potential of V2. This action, together with the drop incathode potential of V2 causes V2 to conduct.

Plate current flow of V2 through its load resistor R3 produces a sharpvoltage drop at the anode of V2 and terminal 1, as shown at c in curve1a. This occurs at the time the negative trigger impulse is applied toV1. This sharp voltage drop is of course transmitted to the control gridof V1, cutting off V1. Since V1 is no longer conducting, the voltagedrop across resistor R1 is smaller so that grid current flows in V2,discharging capacitor C1. the middle curve of Figure 2, and by therising portion d of the upper curve la. When C1 has discharged 'to asufficiently low voltage and the voltage drop across R1 biases V2 tocutoff, the plate voltage of V2 increases rapidly when V1 conducts asindicated at f in curve 1a and the capacitor C1 begins to charge towardB+, repeating the cycle.

Thus, a sawtooth voltage is produced on terminal 2,

as illustrated by the curve 2a of Figure 2. This can be used, forexample, as the sweep voltage in an oscillo scope. At the same time,terminal 1 can be capacitively coupled to the control grid of thecathode ray tube such that fiyback blanking is provided by the voltagedrop sections shown in the upper curve 1a. The negative trigger impulsesof the lower curve 3a are strictly synchronizing signals used withrecurrent operation, as described above.

For triggered monostable operation, switch S is closed, connecting avoltage +31 to capacitor C1 through the diode D such that the voltage oncapacitor C1 cannot rise to the point of conduction in V2 because as thevoltage on the plate side of the diode D exceeds that on the cathode,conduction through D takes place. Thus, the grid potential of V2 is heldjust below its critical point. When a negative trigger voltage ofsufiicient amplitude is now applied to the screen grid of V1, V1 willcease conducting and the voltage drop across resistor R1 becomes zero.Then V2 will conduct because the grid to cathode potential now biasesthe grid of V2 strongly positive. Conduction of V2 discharges capacitorC1 rapidly.

After capacitor C1 discharges, V2 ceases to conduct and V1 beginsconduction, and capacitor C1 immediately begins charging toward B+through resistor R2 forming a sawtooth waveform up to the constantlimiting voltage permitted by diode D. The operation is very similar tothat of recurrent operation as depicted in Figure 2 except that thesawtooth tops of curve 2a are fiat. If negative trigger signals (likethe negative impulses of curve 311, for example) are provided every timeas soon as capacitor C2 reaches the constant limiting voltage permittedby diode D, the waveforms for triggered monostable operation will beidentical to those of Figure 2.

Thus, there is provided a novel sawtooth voltage gen- This isillustrated by the dropping portion b of enumerated 'as desirable, butwhich obviously is susceptible of modification in its form, proportions,detail construction and arrangement of parts without departing from theprinciples involved or sacrificing any of its advantages.

While in order to comply with the statute, the invention has beendescribed in language more or less specific as to structural features,it is to be understood that the invention is not limited to the specificfeatures shown, but that the means and construction herein disclosedcomprise the preferred form of several modes of putting the inventioninto effect, and the invention is, therefore, claimed in any of itsforms or modifications within the legitimate-and valid'scope of theappended claims.

What is claimed is: v

l. A sawtooth voltage generator for both recurrent, free-running andtriggered, monostable operation, comprising: a first electron tubeincluding a cathode, a first control grid, a second control grid and ananode; a second electron tube including a cathode, control grid andanode; means for applying a positive potential to the second controlgrid of said first electron tube; an input connection to said secondcontrol grid for applying control signals thereto; an electrical storageelement connecting the control grid of said second electron tube to areference point of fixed potential; means for providing positivecharging energy to said storage element; means connecting the anodes ofsaid electron tubes to a source of positive potential; means connectingthe cathodes of said electron tubes to said reference point for biasingsaid cathodes relative to said anodes; means for applying theanodepotential of said second electron tube proportionately to the firstcontrol grid of said first electron tube; means for maintaining thecontrol grid of said second electron tube below a fixed predeterminedpotential to prevent conduction thereof in recurrent, free-runningoperation; switching means operable to connect said potentialmaintaining means to the control grid of said second electron tube; andan output connection to said storage element for obtaining a positivesawtooth output voltage, whereby said sawtooth voltage generatorfunctions in recurrent, free-running operation when said switching meansdisconnects said potential maintaining means from the control grid ofsaid second electron tube,

erator which is simple of construction and is capable of both recurrentand triggered operation. Blanking of a fiyback trace is readily anddirectly possible with this invention when employed as a sweep generatorin an oscilloscope. The operation of the sawtooth voltage generator inrecurrent (free-running) fashion can be synchronized by various suitablesignals.

It should be noted that the trigger and synchronizing signals are notlimited to the negative impulses illustrated but can comprise all formsof negative going signals. For example, the spikes (impulses) canobviously be replaced by short duration pulses for triggered operationand a sine wave can be employed as a synchronizing signal.

From the above description it will be apparent that there is thusprovided a device of the character described possessing the particularfeatures of advantage before and in triggered, monostable operation whensaid switching means connects said potential maintaining means to thecontrol grid of said second electron tube.

2. Apparatus in accordance with claim 1 including, in addition, anotherstorage element connected between the anode of said first electron tubeand the control grid of said second electron tube for neutralization ofhigh frequency components in the control signals applied to said inputconnection to said second control grid.

3. Apparatus in accordance with claim 1 including, in addition, anotheroutput connection to the anode of said second electron tube forproviding a substantially square blanking wave therefrom.

4. A sawtooth voltage generator for both recurrent, free-running andtriggered, monostable operation, comprising: a first electron tubeincluding a cathode, con trol grid, screen grid and anode, a secondelectron tube including a cathode, control grid and anode; means forapplying a positive potential to the screen grid of said first electrontube; an input connection to said screen grid for applying negativecontrol signals thereto; a capacitor connecting the control grid of saidsecond electron tube to a reference point of fixed potential; means forproviding positive charging energy linearly to said capacitor; a cathoderesistor connecting the cathodes of "said electron tubes tosaid'r'efere'nce point'for biasing said cathodes relativeto said anodes;plate resistors respec- 'tively connecting the anodes of saidelectron'tubes to a tube; undirectional rectifier means connected toanother source of positive potential for maintaining the control grid ofsaid second electron tube below a fixed predetermined potential toprevent conduction thereof in recurrent, free-running operation;switching means operable to connect said potential maintaining means tothe control grid of said second electron tube; and an output connectionto said capacitor for providing a positive sawtooth output voltage,whereby said sawtooth voltage gen erator functions in recurrent,free-running operation when said switching means disconnects saidpotential maintaining means from the control grid of said secondelectron tube, and in triggered, monostable operation when saidswitching means connects said potential maintaining means to the controlgrid of said second electron tube.

5. Apparatus in accordance with claim 4 including, in addition, a smallcapacitor connected between the anode of said first electron tube andthe control grid of said second electron tube for neutralization of highfrequency components in the control signals applied to said inputconnection to said screen grid.

6. Apparatus in accordance with claim 4 including, in addition, anotheroutput connection to the anode of said second electron tube forproviding a substantially square blanking wave therefrom.

References Cited in the file of this patent UNITED STATES PATENTS2,265,290 Knick Dec. 9, 1941 2,548,953 Crown et al. Apr. 17, 19512,605,406 Bartelink et al. July 29, 1952 2,629,825 Eckert et al Feb. 24,1954 2,688,696 Reeves Sept. 7, 1954 2,721,977 Rich Oct. 25, 1955

